Electric circuit breaker



Oct. 27, 1942. H. E. BRANNON 2,299,728

ELECTRIC CIRCUIT BREAKER Filed Feb. 15. 1940 A [PBEET E 5E4/v/v0/v ATTORNEY.

.Patented Oct. 27, 1942 UNITED STATES PATENT OFFICE 2,299,723 auz'ormc CIRCUIT BREAKER Herbert E. Brannon, Detroit, Mich. Application February 15, 1940, Serial No. 319,009

3 Claims.

This invention relates to automatic electric circuit breakers of the type employing laminated temperature responsive elements as the means for breaking the circuits in which they are incorporated.

The principal object of the invention is to provide a circuit breaker of the type mentioned above which is more accurate and efficient than those previously known by reason of the fact that two independently actuated laminated elements are employed. Another object of the invention is to provide a circuit breaker having means for compensating for variations in ambient temperatures. Another' object is to provide a circuit breaker having a means for breaking the circuit quickly upon the attainment of a predetermined temperature of said means.

These objects .will more fully appear in the fol,- lowing specification, reference being had to the accompanying drawing, wherein:

Figure 1 is a cross-sectional view of a device embodying the invention;

Figure 2 is an exploded cross-sectional view of the device shown in Figure 1;

Figure 3 is a cross-sectional view taken on sub-- stantially the line 3-3 of Figure 1;

Fig ure 4 is a. plan view of one of the laminated elements incorporated in the invention;

Figure 5 is aplan view of a fusible metal link used in the'invention;

Figure 6 is a cross-sectional view of a slightly modified form of the invention; and

Figure 7 is a cross-sectional view of a still further modified form of the invention.

Figures 1 to 5 of the drawing illustrate a circuit breaker having an outer shell III which consists of a body portion II and a base l2. The two parts of the shell are preferably molded from suitable insulating material, such as porcelain or a synthetic resin. The body II is hollow, as shown in Figures 1 and 2- and is substantially cylindrical in cross-section. The side wall of the body is provided with molded threads II! for a purpose which will presently appear. At one side of the body is a notch l4. The inner wall of the body adjacent its open end is provided with an annular rabbet IS.

The base I2 is circular in plan and of the.

wall of the retaining ring is corrugated to form helical threads l8, and has a radial flange H) at one end. The threads l8 cooperate with the threads |3 on the body II and the flange l9 fits over the outer rim of the base 2 to hold the parts together.

Mounted within the rabbet l5 between the body H and the base I2 is a metal ring to which a fusible link 20 is connected, a laminated resistor 2|, an insulating ring 22, a second laminated resistor 23, and a substantially frustoconical terminal element 24, in the order named.

One end of the fusible link 20 is connected to the ring 25. Preferably the link 20 and ring 25 are stamped from one piece of sheet zinc or other suitabl metal of low melting point. The ring 25 has formed in ita plurality of radially extending axially offset grooves 25a, the purpose of which will appear presently. The fusible link 20 has a pair of narrow necks 28. The cross-section of the necks is such that the resistance thereof creates sufiicient heat to melt them if the current flowing therein exceeds a predetermined amount. The free end 21 of the fusible link 20 is bent to lie alongside of the body The laminated metal resistors 2| and 23 are both identical. Each resistor is of cruciform shape having 4 arms 29 radiating from its center, as shown in Figure 4, and is made up of thin sheets of two dissimilar metals 30 and 3| having their adjacent faces intimately secured together. Secured to the center of resistor 2| is a contact 32 of silver, or other suitable material. A similar contact 33 is attached to the center of resistor 23. The metalsheet 3| in each resistor has a low coeflicient of expansion, and the sheet 30 has a high coeflicient of expansion. It will be noted in Figure 2 particularly that th resistors are mounted with the high expansion sides 30 re mote from each other and the low expansion sides 3| adjacent each other.

The insulating ring 22 is simply a cylinder of short axial length formed from any suitable insulating material, such as porcelain or synthetic resin.

The terminal 24 is for the most part frustoconical in shape, but is provided at its upper edge with a radial flange and at its lower end with a. cylindrical tip 34. The tip 34 is adapted to fit within the aperture "5 in the base I2 and project slightly from the outer surface of said base. The

flange 35 has a plurality of downwardly offset radial grooves 36 therein.

The assembly of the various elements previously described is believed to be obvious from an inspection of Figures 1 and 2. The various elements are inserted into the body H in the order shown in Figure 2. The free ends of the arms 29 of the resistors 2| and 23 lie in the grooves 25a and 36 in the ring 25 and terminal element 24 respectively. The arms 29 are loose in their respective grooves to permit the ends of the arms 29 to move slightly in their own planes. The free end 21 of the fusible link extends through the notch I4 and overlies the outer surface of the body II. The retaining ring l1 holds all of the parts together and touches the free end 21 of the fusible link 20, thereby forming one terminal of the circuit breaker. The other terminal is element 24.

The device just described is primarily adapted for use in a standard fuse plug socket, such as is ordinarily found in household wiring systems. When current is flowing in the line it passes from the cylindrical tip 34 of the terminal element 24 out to its rim 35, thence through the arms 29 of the resistor 23 to the contact 33, then to the contact 32 on the resistor 2i, and out through the arms 29 of said resistor 2| into the metallic ring '25. From this point the current flows through the fusible link to the retaining ring I? which forms the other terminal of the device.

The two laminated resistors 2i and 33 have a predetermined resistance to the flow of current through the circuit breaker. Current passing through the resistors causes them to heat up and deflect away from each other because they are so mounted as to deflect in opposite directions. As soon as there is any appreciable movement of the two parts the contacts 32 and 33 move apart, and the circuit is broken.

Since there are two of the laminated resistors, the amount of movement for any given temperature rise will be more than if only one of these elements is used. Accordingly, the circuit will be broken more sharply than it would be if only one were employed, and there will be much less arcing between the contacts.

If the circuit becomes heavily overloaded by reason of a short circuit in the line, the fusible link 20 will melt at either one or both of the necks 28 before the resistors 2i and 23 can reach the predetermined temperature at which they separate, and the circuit will be permanently broken. Thus it will be seen that the device provides a circuit breaker which automatically takes care of small and more or less temporary overloads which occasionally occur in the wiring system without necessitating the replacement of a fuse, yet in the event that the circuit is heavily overloaded the fusible link melts and the circuit is not endangered. a

The structure shown in Figure 6 is similar to that previously described, but difiers primarily in that but one of the two laminated temperature responsive elements is in the circuit and is con sequently a resistor. The other laminated temperature responsive element is responsive to ambient temperature only.

The device comprises a shell 56 having a body and a base 52, the former having threads 53 thereon. The body 5| has a notch 54 in one side wall and an internal rabbet 55 in its open end. Surrounding the body side wall is a retaining ring 56 which holds the base 52 to the body 5!.

Mounted in the rabbet 55 is a metal ring 51, a laminated temperature responsive element 58, an insulating ring 59, a second temperature responsive element 60, in this case a resistor, and

a terminal element 6| in the order named.

The metal ring 51 is a sheet metal ring having offset grooves therein similar to the grooves 25a in the ring 25.

The temperature responsive element 58 is of cruciform shape and made up of two dissimilar metal sheets 62 and 63. Metal sheet 62 is the high expansion side and sheet 63 is the low expansion side of the element. At its center is a contact 64 which is connected directly to one end of a fusible link 65. The other end 66 of the fusible link passes out through notch 54 and touches the retaining ring 56, thereby making the latter one terminal of the circuit breaker.

The temperature responsive element 60, hereinafter called a resistor, is also of cruciform shape and has a contact 61 at its center, normally engaging contact 64. The resistor 68 is made up of three laminated metal sheets 68, 69 and I8. Resistor 60 is designed to have the same expansion characteristics under ambient tempera ture as element 58. Therefore the coefficients of expansion of metallic sheets 68 and 10 of resistor 60 are the same as sheets 62 and 63 respectively of element 58. Sheet 69 of resistor 60 has the same coeflicient of expansion as either sheet 68 or sheet 16, but has a higher resistance. If sheet 69 has the same coeificient of expansion as sheet 68, the combined cross sectional area of the two at any point must be the same as the corresponding cross section of sheet 62 inclement 58, and the cross sectional area of sheet Ill must correspond with that of sheet 63. On the other hand, if sheet 69 has the same coemcient of expansion as sheet 10, then the combined cross section of sheets 69 and 10 must equal that of sheet 63, while the cross section of sheet 68 must be the same as sheet 62.

Thus, the high expansion and low expansion sides respectively of the element 58 and resistor 60 are the same in cross-section and have the same expansion characteristics for a given ambient temperature change. However, in resistor 60 either the high or the low expansion side is composed of two sheets of metal having the same coefiicient of expansion and different resistances.

The terminal element BI is identical to the terminal element 24 previously described and has a tip H projecting through an aperture in the base 52.

In the structure just described the path of the current is through the terminal element 6|, then through resistor 60 to contact 61. From this contact 61 is passes to contact 64 and directly into the fusible link 65 from which it passes to retaining ring 56, the other terminal of the device.

Thus it will be seen that temperature responsive element 58 is not in the circuit. Its sole purpose is to compensate for variations in the ambient temperature of the laminated temperature responsive elements. It deflects in the same direction as resistor 60 under a corresponding temperature change.

The presence of the high resistance center metal sheet 69 in the resistor 60, causes it to attain a high temperature in a relatively short time when current flows through it. This results in a greater deflection of the entire resistor 60 than would be obtained with a similar resistor of bimetal. When current passes through it, the resistor 60 attains a much higher temperature than element 58. Therefore, even though element 56 deflects slightly under an increase in the ambient temperature, resistor 60 deflects more and will break the circuit when the current passing through it reaches a predetermined quantity.

Figure 7 shows another modified form of the invention. It comprises a shell I consistin of a body IN and a base I02. annular groove I03 at its open end.

Located within the groove I03 is a fusible link I 04, identical with link 20, and having one end connected to a ring I 05. Next to the ring is a laminated resistor I06, then an insulating ring I 01, another laminated resistor I08, and flnally'a terminal element I09 having a cylindrical tip IIO projecting through an aperture in the base I02. A retaining ring III is mounted over the shell in the same manner as the ring I1 in Figures 1 and 29nd held in place by threads II2 on the body IOI.

The resistors I06 and I08 are of cruciform shape, the same as resistor 29 in Figure 4, and are provided with contacts H3 and H4 respec tively at their centers. Resistor I06 is made up of two dissimilar metals H5 and IIS, and resistor I08 consists of two dissimilar metals II 1 and H8.

The two resistors are made of metals such that the coefficient of expansion of each resistor is the same, but their internal resistances are different, that of resistor I06 being greater than resistor I08. Furthermore, the resistors are mounted so that the low expansion side of resistor I05 is adjacent the high expansion side of resistor I08. In other words, metals I I6 and I I8 have lower coefllcients of expansion than metals I I5 and I I1 respectively.

When the circuit breaker is connected into an electric circuit, the path of the current is the same as that in the device shown in Figures 1 and 2. It flows from the tip I I0 through the entire terminal element I09, and then through the arms of resistor I08 to the contact II4. From contact II 4 it flows to contact II3, through the arms of resistor I 06 to the ring I05, and finally through link I04 to the retaining ring I I I, the latter being the other terminal of the circuit breaker.

Thus it will be seen that when a current passes through the device both resistors are heated because of their resistance to the flow of current, and both resistors deflect in the same direction. Because resistor I 08 has ahigher resistance than resistor I08, the former attains a higher temperature and consequently deflects more than the other resistor, thereby breaking the circuit. However, since the coeflicients of expansion are the same, any change in ambient temperature within the shell will cause a corresponding deflectlon in both resistors, thereby compensating for variations in ambient temperature.

In all three of the modifications disclosed the laminated temperature responsive elements are designated as of cruciform shape. and element 2| is shown as having four arms. This particular shape, however, is not essential, and there may be more or less than four arms. In each case, however, the laminated element must be sup- The body IOI has an a ported at the extremities of its arms, and the contact must be mounted remote from the extremities, preferably at the center. Furthermore, the arms must be supported on the shell loosely enough to permit a slight movement of the ends of said arms in their own plane, to permit the element to deflect.

From the foregoing it will be apparent that the basic feature of the invention is in the provision of two laminated temperature responsive elements acting independently of each other. results in a quick acting circuit breaker in which provision is made for counteracting the effect of ambient temperatures and thereby providing a very accurately controlled device.

The scope of the invention is indicated in the appended claims.

I claim:

1. A circuit breaker comprising an insulating support, two spacedterminals on said support a last mentioned layers having a greater resistance than the other, each of said elements having a contact thereon normally touching each other and adapted to separate upon a predetermined increase in the temperature of said a connection between one of said terminals and said resistor element at a point remote from the contact thereon and a connectioibetween the other element and the other terminal.

2. A circuit breaker comprising a shell, two spaced terminals supported by a wall of said shell, a pair of laminated temperature responsive resistors each comprising a central portion and a plurality of arms radiating therefrom, said resistors being mounted within the shell and supported thereon solely by the extremities of the arms for limited movement of the latter in the planes of the resistors, said resistors being adapted to deflect in the same direction upon a corresponding change in the temperatures thereof, said resistors having contacts thereon adjacent their centers normally touching each other, a connection between one of said terminals and one of said resistors at a point remote from the contact thereon, and a connection between the other terminal and the other resistor at a point remote from its contact, one of said resistors being adapted to deflect more than the other upon a predetermined change in the current flowing through them. I

3. A circuit breaker comprising a shell, two spaced terminals-supported by a wall of said shell, a pair of laminated temperature responsive elements each comprising a central portion and a plurality of arms 'radiating therefrom, said elements being mounted within said'shell and supported thereon solely by the extremities of the arms for limited movement of the latter in the planes of the elements, one of said elements being an electrical resistor composed of three layers of metal, two of said layers having the same 00- efllcient of expansion and one of said last mentioned layers having a greater resistance than the other, each of said elements having a contact thereon normally, touching each other and adapted to separate upon a predetermined increase in the temperature ment, a connection between oneof said terminals and said resistor element at a point remote from the contact thereon, and a connection between the other element and the other terminal.

HERBERT E. BRANNON.

of said resistor ele- 

